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# I need help with few parameters in MCE Wizard

Level 3
Level 3

I am working on a BLDC motor controller using IMC302AF064XUMA1 microcontroller.

I need help in calculating values for the below questions:

Q83. Motor 1 current input scaling

Q84. Internal current feedback amplifier gain

Q85. Motor 1 current input to ADC offset voltage

My op amp gain for current sense circuitry is 34 and my shunt resistor value is 3mE.

This is the information I have on the motor:

1. Rated Amps: 8A Rated / 11A peak
2. Number of poles: 6Poles
3. Motor stator per phase winding resistance: 0.1E
4. Motor Lq inductance: 0.133mH
5. Motor Ld indictance: Ld=Lq
6. Motor Back Emf Constant(Ke): (calculated ourselves and found to be 4.007 (ln-rms)/krpm)
7. Motor max RPM: 1500RPM
8. Rated speed: 1000 RPM
9. Minimum running speed of the motor: 200RPM
10. Speed ramp rate (rate of increase and decrease in speed): Minimum 1RPM/0.1ms
11. Target DC bus voltage at the time of initialization: 36V

1 Solution

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Hello @cw2611  and @Waseem ,

I have a few points to say.

1. Motor Max RPM has been given as 1500rpm. In Question9 - Minimum Running Speed, kindly set the minimum speed between 5-10% of the rated speed which is the recommended value while using flux PLL based angle estimation.
2. The low speed threshold speed (Question 13) has been set to 200rpm and the low speed current limit has been set to 4A, please set the value of low speed current limit at the minimum speed, not at the value of the low speed threshold speed.
3. The value of DC Bus Critical Overvoltage level is supposed to be more than that of DC Bus Over Voltage level and lesser than that of the Maximum DC Bus Voltage.
4. Kindly verify the value of VMCU and also the path of the signal OC_BK.
5. I see that the non inverting opamp circuit with a gain of 33 has been used for current feedback, and the value of Rs is 2.5m-ohm. The gain value to be entered in Question 83 is 82.5 mV/A.
6. The input to the internal ADC of the imotion IC is a unipolar signal and I don't see any bias added to the output of opamp. Kindly add the bias circuit to avoid any damage to the IMC302.
7. As explained in the comments above, the product of internal gain and the bias HAS TO BE VDD/2, otherwise it will cause error in the internal current calculations. Please rectify this.
8. Enable DC Bus Compensation (Question 68).
9. Kindly check the value of Flx_M in the MCE Designer. It is supposed to be 2048. Also, enable the flux PLL error (Quetion 70) at a later stage when other things are verified.
10. Current rating of the motor is 8A, Motoring current limit set is 7.2A and the Overcurrent Trip level for the Gatekill Comparator is set as 5A. Kindly look back into these and verify.
11. Kindly refer to section 4.2 of the iMOTION™ Software Reference Manual and section 3.2 of AN2020-12 for some more information on control loop tuning.
Best Regards,
Sai
13 Replies

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Hello @cw2611 ,

Please share the schematics of the hardware and also the MCE Wizard .mc2 file so that we can get back with the calculations.

Best Regards,
Sai
Attachments are accessible only for community members.

Level 3
Level 3

# Re: I need help with few parameters in MCE Wizard

Level 3
Level 3

I have replaced the gate driver with 3 H-bridge ICs since we were having issues with the one mentioned in the schematic. I have attached the schematic of the OP AMP section for current sense.

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Hello @cw2611 ,

Thanks for letting us know about the change.

Q83. Motor 1 current input scaling
1. This value is basically the gain term, excluding of the signal which goes to the pins 18,15,11 (IU, IV, IW respectively).
2. The input to the ADC can lie only between 0 and 3.3V (controller supply voltage) and as the current is a bipolar signal, it needs to have a gain as well as an offset.
3. In the previous case of the smart gate driver, the input to the ADC would have been (0.003*Gain set to the gate driver) + (VAUXCC/2).
4. In the updated circuit, I can see that the  non inverting opamp gain is 33 and there is no offset added. please add the offset accordingly.
5. Were only SPA, SPB, SPC from the schematics is given to the non inverting terminal of the opamp? The gain is 33, and the value that needs to be entered is 0.003*33 = 0.099.

Q84. Internal current feedback amplifier gain
1. This value gets multiplied with the external gain. Say that the external gain and offset are G_ext and Off, and the value of internal gain is G_int, then the value of analog input to the ADC is (G_int*G_ext*current)+ (G_int*Off).
2. The value of the (G_int*Off) must be VDD/2 (VDD = Controller supply voltage) and the gain term must be less than VDD/2. VDD = Controller supply voltage, 3.3V in this case.

Q85. Motor 1 current input to ADC offset voltage
This is the value of the offset of the external scaling circuit. Please include an offset in your feedback so that the input to the ADC is a unipolar signal only. Leg shunt current is a bipolar signal.

Best Regards,
Sai
Attachments are accessible only for community members.

# Re: I need help with few parameters in MCE Wizard

Level 3
Level 3

Hey @psb !

I uploaded the parameters and tried driving the motor. The motor did spin 2 revolutions and "DC BUS LOW VOLTAGE" fault was triggered. What could be wrong? Where should I start looking for first?

I had supplied 36V/2.5A from a regulated power supply. The motor's operational voltage is 30VDC - 50VDC and rated at 8A and 11A peak current capability.

I have attached the parameter file that was uploaded to MCE designer. Please check.

Also, please let us know the important parameters to look out for.

Level 3
Level 3

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Hello @cw2611

What was the value of DC bus voltage from the time the motor started till the time the fault occurred and also the input current to the inverter ? Please share the waveforms as well, for a better understanding.
The input voltage of the DC source must have decreased as the  phase current drawn by the motor must have been more than the 2.5A current limit set in the DC supply. Kindly increase the input current limit to a value more than the phase current drawn by the motor at your test conditions and confirm back.

Best Regards,
Sai

# Re: I need help with few parameters in MCE Wizard

Level 3
Level 3

I had set 36V/2.5A in the regulated power supply. When the motor was run with another motor controller, it consumed less than 1A current.

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator
• What is the value of input current to the inverter, motor current and also the DC voltage when the fault occurred with IMC302AF064XUMA1.
• Kindly share the updated schematic as well, so that we can re-verify all the configuration parameters like current and voltage sense gains entered in the MCE Wizard.
• Are the PI controller values for speed and current loops same in both IMC302AF064XUMA1 and the other controller ?
Best Regards,
Sai

# Re: I need help with few parameters in MCE Wizard

Level 3
Level 3

Hey @psb !

Here are the waveforms when the drive is started.

All the waveforms appear similar when zoomed in.

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Can you please give details of what waveforms these are of and under what condition (start to end) have they been captured ? Also,

• What is the value of input current to the inverter, motor current and also the DC voltage when the fault occurred with IMC302AF064XUMA1.
• Kindly share the updated schematic as well, so that we can re-verify all the configuration parameters like current and voltage sense gains entered in the MCE Wizard.
• Are the PI controller values for speed and current loops same in both IMC302AF064XUMA1 and the other controller ?
Best Regards,
Sai
Attachments are accessible only for community members.

# Re: I need help with few parameters in MCE Wizard

Level 1
Level 1

Hi @psb

• The waveforms are in the order U_Phase(2nd,3rd pic), V_phase(1st) pic, W_phase(3rd) pic.
• Input current to the inverter is around 0.521A
• Motor rated current is 8A
• DC voltage at the inverter side is appx 38V on H-bridge side
• We kept the P value for speed regulator(Q.62) around 1 and I value for  speed regulator (Q.63) 45.23 rad/sec. The other controller which we used runs with trapezoidal commutation hence PI speed loops are not present in it.

Here we are able to rotate the motor only 2-3 revolutions only in sensor less mode after that we get gatekill fault. Also when we place some load, the motor instantly stop with gatekill fault.

For the schematic part we use different schematic for H-bridge and current sense. I have also attached our parameter and .mc2 file for your reference.

# Re: I need help with few parameters in MCE Wizard

Moderator
Moderator

Hello @cw2611  and @Waseem ,

I have a few points to say.

1. Motor Max RPM has been given as 1500rpm. In Question9 - Minimum Running Speed, kindly set the minimum speed between 5-10% of the rated speed which is the recommended value while using flux PLL based angle estimation.
2. The low speed threshold speed (Question 13) has been set to 200rpm and the low speed current limit has been set to 4A, please set the value of low speed current limit at the minimum speed, not at the value of the low speed threshold speed.
3. The value of DC Bus Critical Overvoltage level is supposed to be more than that of DC Bus Over Voltage level and lesser than that of the Maximum DC Bus Voltage.
4. Kindly verify the value of VMCU and also the path of the signal OC_BK.
5. I see that the non inverting opamp circuit with a gain of 33 has been used for current feedback, and the value of Rs is 2.5m-ohm. The gain value to be entered in Question 83 is 82.5 mV/A.
6. The input to the internal ADC of the imotion IC is a unipolar signal and I don't see any bias added to the output of opamp. Kindly add the bias circuit to avoid any damage to the IMC302.
7. As explained in the comments above, the product of internal gain and the bias HAS TO BE VDD/2, otherwise it will cause error in the internal current calculations. Please rectify this.
8. Enable DC Bus Compensation (Question 68).
9. Kindly check the value of Flx_M in the MCE Designer. It is supposed to be 2048. Also, enable the flux PLL error (Quetion 70) at a later stage when other things are verified.
10. Current rating of the motor is 8A, Motoring current limit set is 7.2A and the Overcurrent Trip level for the Gatekill Comparator is set as 5A. Kindly look back into these and verify.
11. Kindly refer to section 4.2 of the iMOTION™ Software Reference Manual and section 3.2 of AN2020-12 for some more information on control loop tuning.
Best Regards,
Sai